I haven't run it, but I think your code will error on the line
because deltaxj(i,ii,iii) is a number, so has one element, and dn is an array which grows with every iteration. You can't assign an array element to be equal to an array.
I suspect you intended
As a side note, please choose better names for your loop indices. Firstly, i is a bad variable name because it already has a built-in value, and secondly, it's difficult to tell at a glance what the difference between (ii,iii) and (iii,i) is (for example). If you really need to use that many nested loops (rather than vectorising your code), I'd suggest using k1, k2, k3, or similar.